How do I adjust the idle speed on a 91 samurai.  Mine idles at about 1500.  Shouldn't it be more like 800?

There is a screw on the front of the throttle body that you can adjust.  It is usually covered by a black rubber plug. Generally, you aren't supposed to adjust it...but if you have checked everything to make sure everything is operating correctly, then adjusting it is probably your only option. You are talking about warm/hot idle right?  Because cold idle should be right around 1500....or at least that is where I like to set my cold idle.

Before you change the idle setting, check your gages.  Is the engine coming up to temperature. 

My Sami had a bad thermostat that didn't close and the engine was running cold.  This resulted in the choke circuit not closing, and that kept it at high idle all the time.

I know on the toyota 22r if the coolent is to low causes the idle circuit to run a fast idle on a efi motor

Also, you could have a vacuum leak and the computer will compensate and raise the idle. On an EFI system, mechanically adjusting the idle should be the last thing you check/do... It's changed because something is wrong. They are adjusted and 'sealed' at the factory.

Good luck, Eric